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Title Right Middle Lobe Atelectasis: Chest Radiographic and CT AppearancesCorrelating with the Clinical Features

Author(s) Miyazaki, Atsushi; Ashizawa, Kazuto; Mori, Masakazu; Ohtsubo, Mayumi

Citation Acta medica Nagasakiensia. 2003, 48(3-4), p.159-166

Issue Date 2003-12-24

URL http://hdl.handle.net/10069/16261

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Acta Med. Nagasaki 48: 159-166

Right Middle Lobe Atelectasis: Chest Radiographic and

CT Appearances Correlating with the Clinical Features

Atsushi MIYAZAKI 1,2), Kazuto ASHIZAWA 2), Masakazu MORI 1), Mayumi OHTSUBO1)

1) Department of Radiology, Japanese Red Cross Nagasaki Atomic Bomb Hospital

2) Department of Radiology and Radiation Biology, Nagasaki University Graduate School of Biomedical Sciences

Purpose: To evaluate chest radiographic and CT findings of

right middle lobe (RML) atelectasis correlating with the

clinical features.

Materials and Methods: We reviewed 47 patients with RML

atelectasis and classified their chest radiographic findings

into four types (Type 1-4) based on the shape of the opac-

ity. The degree of RML atelectasis was classified into three

types according to CT findings, namely severe (>90%), mod-

erate (50-90%), and mild (10-50%). Then we correlated them

with chest radiographic types and patient's symptoms.

Results: In severe atelectasis (n=10), no definite abnormali-

ties were detected on chest radiographs (Type 1). In moder-

ate atelectasis (n=24), 14 cases (58%) showed triangular

opacity (Type 2) and nine cases (38%) showed band-like

opacity (Type 3) along the right cardiac border. In mild

atelectasis (n=13), 11 cases (85%) showed vague opacity at

the right lower lung field (Type 4). In severe atelectasis,

only one case (10%) had symptoms. In contrast, 14 cases

(58%) in moderate atelectasis and six cases (46%) in mild atelectasis had symptoms.

Conclusion: Our results indicate that RML atelectasis has a

very wide spectrum of imaging finding of chest radiograph

and CT, and patient's symptoms are related to the degree

of atelectasis.

ACTA MEDICA NAGASAKIENSIA 48: 159-166, 2003

works we have often noticed that RML atelectasis

varies greatly from case to case in its radiographic ap-

pearances. Some cases can only be diagnosed by CT.

Clinical presentations of RML atelectasis also have

many variations. There have been many reports de-

scribing various aspects of both clinical and imaging

features of RML atelectasis. However, there has been

no study correlating the imaging findings and clinical

features. The purpose of this report is to describe the

results of our investigation of radiographic and CT

appearances of RML atelectasis correlating with the

clinical features.

Materials and Methods

Key Words: middle lobe atelectasis, chest radiograph, chest CT

Introduction

Right middle lobe (RML) atelectasis is one form of

the lobar collapses, and has been well known both to clinicians and radiologists. It has often been called "right middle lobe syndrome" . At our daily clinical

Address Correspondence: Atsushi Miyazaki, M.D.

Department of Radiology, Japanese Red Cross Nagasaki

Atomic Bomb Hospital, 3-15 Mori, Nagasaki, 852-8511, Japan

TEL: +81-95- 847-1511, FAX: +81-95- 847-8036

E-mail: [email protected]

Eighty hundred seventy three cases were examined on chest CT scan in our hospital between 1996 and

2000. According to our CT records, 182 patients had RML atelectasis, and both chest radiographs and CT

films were available in 108 patients out of them. Some cases, with concomitant severe involvement by

other disease or postoperative change were excluded. 56 cases showing only slight volume loss (less than

10%) on CT were also excluded. The remaining 47 pa-tients were included in this study. Fourteen were men

and 33 were women. The age ranged from 14 to 87

years with a mean age of 64 years. Clinical informa-tion of the patients was obtained from their medical records. The bronchi were patent in all of the 47

cases. Lateral chest radiographs, available in 18 pa-tients, were not analyzed. Parameters for PA chest ra-

diograph were 105 KVp and 4-10 mAs. CT with heli-cal scanning was performed at 120 KVp and 100 mAs,

5-mm collimation, pitch 1.4, and 7-mm reconstruction intervals. All CT scans were obtained on a X-Vigor

(Toshiba Medical Systems, Tokyo, Japan). All scans were obtained at end-inspiratory lung volumes and

photographed at window levels and widths appropri-ate for lung parenchyma (level, -700 HU; width, 1800 HU) and mediastinum (level, 25 HU; width, 430 HU).

Atsushi Miyazaki et al : Radiographic and CT Appearances of Right Middle Lobe Atelectasis

Two experienced radiologists interpreted chest radio-

graphs and CT in 47 patients. Posteroanterior (PA) chest radiographs of RML

atelectasis were classified into four types (Fig. 1). In

Type 1, no abnormalities were detected or only slight obliteration of the right cardiac border was seen. In

Type 2, a triangular opacity was seen with its base on the right cardiac border. In Type 3, a band-like opac-

ity was seen along the right cardiac border. In Type 4, there was a small vague opacity near the right car-

diac border. The degree of volume loss of RML was classified into three types according to CT findings; namely, severe, moderate and mild. Volume loss of 90

percent or more was defined as severe, between 50 and 90 percent as moderate, and between 10 and 50

percent as mild. The judgment was made visually, taking the appearances of whole lung fields into con-

sideration. Figure 2 shows a schematic drawing of CT classification of RML atelectasis, at the levels of the

RML bronchial bifurcation and the right inferior pul-monary vein.

Correlation was made between the degree of atelectasis and chest radiographic classification. Correlation was

also made between the degree of atelectasis and the symptoms of patients.

Results

Table 1 shows correlation between the degree of

volume loss and chest radiographic classification. All

ten cases of severe atelectasis were classified as Type 1 showing either no abnormality or only slight oblit-eration of the right cardiac border on PA chest radio-

graph. The lung fields were clear in all ten cases. Even on CT, in severe RML atelectasis, a small trian-

gular opacity with mild bronchiectasis was the sole finding that could be easily overlooked (Fig. 3). In

moderate atelectasis (n=24), 14 cases (58%) showed a triangular opacity as Type 2 (Fig. 4) and nine cases

(38%) showed a band like opacity as Type 3 (Fig. 5) on PA chest radiograph. One case (4%) of moderate

atelectasis showed a vague opacity near the right car-diac border as Type 4 (Fig. 6). In mild atelectasis

(n=13), 11 cases (85%) showed a localized vague opac-ity near the right cardiac border as type 4 (Fig. 7). In

the remaining two cases, triangular opacity was re-vealed along the right cardiac border as Type 2 on

PA chest radiograph. Table 2 shows the correlation between the degree of

Table 1. Correlation between the degree of atetelectasis and

chest radiographic classification

Typel Type2 Type3 Type4

Figure 1. Classification of chest radiographic appearances.

The visualization of minor fissure and right cardiac border

was not taken into consideration in this classification.

Chest radiographic classification

Degree of atelectasis (on CT) Type 1 Type 2 Type 3 Type 4

Severe 10

Moderate 14 9 1

Mild 2 11

Total 10 16 9 12

Table 2. Correlation between the degree of atelectasis and

the presence of symptomsLevel of RML bronchus

Level of Inferior PV

Severe Moderate Mild

Figure 2. Classification of chest CT appearances.

RML: right middle lobe PV: pulmonary vein

Symptoms

Degree of atelectasis (on CT) present absent

Severe 1 9

Moderate 14 10

Mild 6 7

Total 21 26

* Symptoms include cough, sputum, bloody sputum and chest pain.


Figure 3a. Severe RML atelectasis in a 57-year-old woman with no symptoms (medical checkup case). The right cardiac border is clear and no abnormalities can be pointed out on PA chest radiograph. (Type 1)

Figure 4a. A case of moderate RML atelectasis. The patient is an 87-year-old woman with cough and sputum. The right cardiac border is obliterated by a triangular opacity on PA chest radiograph. (Type 2)

Figure 3b. Atelectasis is so severe that the shrunken RML

can only be seen at the level of proximal bronchi of RML on

CT.

Figure 4b. A• broad triangular opacity with bronchiectasis is

seen at the level of RML bronchus on CT.

Figure 3c. RML atelectasis is not shown at the level of infe-

rior PV, 14 mm caudal to 3b.

Figure 4c. 14 mm caudal to 4b. A broad triangular opacity

contacting with the right cardiac border is observed.


Figure 5a. A case of moderate RML atelectasis. The patient

is a 56-year-old woman with cough and hemosputum. A

band-like opacity is observed along the right cardiac border

on PA chest radiograph. (Type 3)

Figure 6a. A case of moderate RML atelectasis. The patient is a 49-year-old man with no symptom in medical checkup. On PA chest radiograph a vague opacity (arrow) is seen near the right cardiac border, and cardiac border is totally obliter-ated. The minor fissure shows slight downward displacement (arrow head). (Type 4)

Figure 5b. An irregular opacity with bronchiectasis is seen at

the level of RML bronchial bifurcation on CT. Centrilobular

small nodules are observed in the lingula of the left upper

lobe.

Figure 6b. A broad transverse opacity extending laterally is

seen between the right upper and lower lobes at the level of

RML bronchus. A small opacity is noted in the lingula.

Figure 5c. An oval opacity contacting with the right cardiac

border with bronchiectasis is seen at the level of inferior PV

in RML. Liner opacities are observed in the lingula, 14 mm

caudal to 5b.

Figure 6c. A broad triangular opacity having wide contact

with the right cardiac border is noted at the level of inferior

PV on CT, 21 mm caudal to 6b.


atelectasis and the presence of symptoms. In severe atelectasis, 1 out of 10 cases (10%) had symptoms. In

moderate atelectasis, 14 out of 24 cases (58%) had symptoms. In mild atelectasis, 6 out of 13 cases (46%)

had symptoms. The presenting symptoms included cough, sputum, bloody sputum and chest pain. Some

patients had more than one symptom, and the sever-ity of the symptoms varied from case to case. Ten out

of 47 cases underwent bronchoscopy and 2 cases were diagnosed as having mycobacterial infection.

Discussion

Figure 7a. A case of mild RML atelectasis. The patient is a 59-year-old woman with no symptom. On PA chest radio-

graph, a small vague opacity near the right cardiac border is noted. (Type 4)

Figure 7b. Aeration is maintained at the level of RML bron-

chial bifurcation on CT_

Figure 7c. A small opacity with bronchiectasis is observed

along the right cardiac border at the level 42 mm caudal to

7b. Similar opacity is seen along the left cardiac border in

the inferior portion of the lingula.

Graham and his associates coined the term "middle

lobe syndrome" and reported 12 cases in which there

was compression of the RML bronchus secondary to

enlarged lymph nodes. Pathologically, the lobes were

atelectatic with varying degrees of interstitial fibrotic

changes and bronchiectasis. Their patients were seen

with hemoptysis, chronic cough, and recurrent epi-

sodes of pulmonary infection''. Since then there have

been many reports describing various aspects of this

disease entity including its etiology, pathophysiology

as well as symptoms. The definition and usage of the

term "middle lobe syndrome" has been debated 2 - 4'. A

term "atelectasis syndrome" has been proposed by

Ring-Mrozik ", but we consider the simple term "right

middle lobe atelectasis" is the most appropriate, to in-

clude all the cases in which there is volume loss of

the RML, minimal to marked, regardless of the cause

and clinical presentation.

Many theories have been proposed regarding the

reason why atelectasis easily occurs in the RML in

comparison with other lobes. RML bronchus is sur-

rounded by the lymph nodes that drain the middle as

well as the lower lobes, and compression of the RML

bronchus is often a consequence of chronic infection

and lymphadenitis 6'. Relatively long length of the RML

bronchus before it divides into segmental bronchi" and

relatively narrow caliber of the RML bronchus as

compared to other lobes" are also described.

Moreover, the RML bronchus arises from the interme-

diate bronchus at almost right angle, causing poor

drainage". All of these factors may predispose the

RML bronchus to its obstruction.

The other important factor is a lack of collateral

ventilation. Bradham proposed that complete fissures

surrounding the RML interfere with the rapid resolu-

tion of an inflammatory process". Culiner hypothe-

sized that an inflammatory process first produces se-

cretions that obstruct the airways in the RML and

that absent or ineffective collateral ventilation results


in alveolar collapse of the lung parenchyma distal to

the obstructed airways". Inners proposed that a high resistance and a long-time constant relative to the

upper lobes characterize collateral ventilation of the RML, because ratio of pleural surface to nonpleural

surface is greater in the RML than in the upper lobes"'. So they suggested that ineffective collateral ventila-tion is a major factor in the pathophysiology of the

RML atelectasis'°' Both chest radiographic and CT findings of RML

atelectasis have been described. With various degree of volume loss, the imaging findings of RML

atelectasis vary greatly. The diagnosis of RML atelectasis is one of the most difficult tasks on PA

chest radiographs. The difficulty in detecting atelectasis in this projection is related to the obliquity

of the atelectatic lobe to the superoinferior plane and the thickness of the collapsed lobe itself"'. There are

some articles that have correlated the chest radio-

graphic findings with the CT findings"-"' but there is no article that has correlated the degree of volume

loss with clinical significance of RML atelectasis. We have demonstrated in this study that in severe

atelectasis, no abnormalities are detected or only slight obliteration of the right cardiac border is seen

on PA chest radiograph. Because the shrunken middle lobe is very small, there is no discernible increase in

opacity. Moreover, because the right upper and/or lower lobes show compensatory expansion, the greater

part of the right cardiac border becomes clearly visi-ble on PA chest radiograph and CT in severe

atelectasis of the RML. Felson pointed out that oblit-eration of the right cardiac border is a useful radio-

graphic finding and can be the clue to the diagnosis of RML collapse"'. However there are cases of RML

collapse in which the right cardiac border is clearly identified on PA chest radiograph"). In moderate

atelectasis, most cases revealed triangular or band-like opacity on PA chest radiograph. These cases revealed

broad triangular or mass like opacity on CT. In one case of moderate atelectasis, PA chest radiograph re-

vealed vague opacity near the right cardiac border and downward displacement of the minor fissure. CT

showed a thin tenting that was directed from the hilum to the periphery at all levels. We speculate that

it was due to pleural adhesion at the lateral side. In mild atelectasis, many cases showed discernible in-

crease in density near the right cardiac border on PA chest radiograph. On CT of these cases, the volume

loss of the medial segment of RML was severer than that of the lateral segment. According to Inners's re-

port, ineffective ventilation of the medial segment is a factor of this condition10' . Two cases of mild

atelectasis showed a triangular opacity as Type 2 on PA chest radiograph. These cases showed moderate

medial segmental collapse and maintained aeration of the lateral segment on CT.

The symptoms and signs in patients with the RML atelectasis included cough, hemoptysis, dyspnea, chest

pain, audible wheezing, and fever and chills. These symptoms, reflecting the presence of pneumonia, were

often intermittent and recurrent despite antibiotic therapy. In some cases, symptoms were absent and the middle lobe atelectasis was discovered on routine

chest radiograph"'. Albo and Grimes reported 30 pa-

tients with "right middle lobe syndrome" who stopped smoking for nine months or longer after the diagnosis.

Complete clearing was seen in 25 of the 30 patients. Symptoms disappeared in the remaining five patients, although their radiographs did not change"'.

This is the first report describing the correlation be-tween the degree of RML atelectasis and patient's

symptom. In our study, in moderate and mild atelectasis, approximately half of the patients pre-

sented respiratory symptoms. On the other hand, most

patients with severe RML atelectasis did not have any symptom. Although the diagnosis of severe RML atelectasis is often very difficult on routine PA chest

radiograph, missing severe RML atelectasis may not result in serious clinical problems.

However we have experienced an interesting case of severe RML atelectasis with adenocarcinoma in pre-

surgery examinations (Fig. 8). On PA chest radiograph and CT, there are two nodules, and they appear to be

located in RML. However, RML shows complete col-lapse as indicated by arrows. Therefore the two nod-

ules, both representing adenocarcinoma, are located in RUL, not in RML. In this way, in severe RML

atelectasis there is a possibility of misdiagnose of loca-tion of the disease, so we should be careful not to overlook this pathologic condition.

During this research work, the authors were im-

pressed by the wide spectrum of imaging findings of RML atelectasis. Classification of RML atelectasis was not easy. We believe our classification was successful,

simplifying RML atelectasis into four types based on

PA chest radiographic appearances and into three de-

grees based on CT findings. There are a number of limitations in this study.

Firstly, correlation between the imaging findings and

laboratory data was not conducted because of the small total number of cases of RML atelectasis.

Secondly, lateral chest radiographs were not analyzed because of their small number. However we believe

that analyzing PA chest radiographs alone is worth-while, particularly because lateral chest radiographs


Figure 8a. The patient is an 80-year-old woman. There is no

obliteration of right cardiac border. There is a nodule in the

right lower lung field.

Figure 8c-2.

Figure 8b. On lateral chest radiograph, the same nodule is lo-

cated in anteroinferior portion of the lung.

Figure 8c-3.

Figure 8c-1. On CT, there are two nodules (arrow), and they appear to be located in the RML. In fact, RML shows com-plete collapse as indicated by arrows heads. The two nodules, both representing adenocarcinoma are located in RUL, not in RML.

Figure 8c-4.

are seldom obtained in actual medical practice these

days. Finally, no case of RML atelectasis associated

with tumor was included. This should be investigated

separately.

In conclusion, we have shown in this article, RML

atelectasis has a very wide spectrum in terms of imag-

ing findings of chest radiograph and CT, and patients'

symptoms are related to the degree of atelectasis.

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